Allowance for loan losses and credit quality Impaired Loans by Class (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
With an allowance recorded, Recorded Investment		$ 1,991	$ 433
With an allowance recorded, Principal Balance		2,023	444
Related Allowance		196	66
With no allowance recorded, Recorded Investment	[1]	3,250	3,992
With no allowance recorded, Principal Balance	[1]	3,902	4,688
Total, Recorded Investment	[1]	5,241	4,425
Total, Principal Balance	[1]	5,925	5,132
Total, Average Recorded Investment		4,488	3,884
Total, Interest Income Recognized		286	175
Government Guarantees on Impaired Loans		587	641
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With an allowance recorded, Recorded Investment		218	228
With an allowance recorded, Principal Balance		228	238
Related Allowance		39	47
With no allowance recorded, Recorded Investment	[1]	1,297	1,450
With no allowance recorded, Principal Balance	[1]	1,832	2,039
Total, Recorded Investment	[1]	1,515	1,678
Total, Principal Balance	[1]	2,060	2,277
Total, Average Recorded Investment		1,625	1,730
Total, Interest Income Recognized		149	65
Construction Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Related Allowance		0	0
With no allowance recorded, Recorded Investment		223	119
With no allowance recorded, Principal Balance		241	135
Total, Recorded Investment		223	119
Total, Principal Balance		241	135
Total, Average Recorded Investment		159	88
Total, Interest Income Recognized		4	4
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With an allowance recorded, Recorded Investment		1,762	193
With an allowance recorded, Principal Balance		1,783	193
Related Allowance		149	9
With no allowance recorded, Recorded Investment	[1]	1,442	2,083
With no allowance recorded, Principal Balance	[1]	1,539	2,174
Total, Recorded Investment	[1]	3,204	2,276
Total, Principal Balance	[1]	3,322	2,367
Total, Average Recorded Investment		2,382	1,699
Total, Interest Income Recognized		110	77
Commercial [Member]
Financing Receivable, Impaired [Line Items]
With an allowance recorded, Recorded Investment		11	12
With an allowance recorded, Principal Balance		12	13
Related Allowance		8	10
With no allowance recorded, Recorded Investment	[1]	288	340
With no allowance recorded, Principal Balance	[1]	290	340
Total, Recorded Investment	[1]	299	352
Total, Principal Balance	[1]	302	353
Total, Average Recorded Investment		322	367
Total, Interest Income Recognized		$ 23	$ 29

[1] Does not reflect government guaranties on impaired loans as of December 31, 2019 and 2018 totaling $587 thousand and $641 thousand, respectively.